Ephemeral bonding

ABSTRACT

Compositions suitable for temporarily bonding two surfaces, such as a wafer active side and a substrate, are disclosed. Methods of temporarily bonding two surfaces, such as the active side of a wafer and a substrate using the compositions disclosed herein are also provided.

The present invention relates to the field of semiconductor manufacture,and more particularly to the temporary bonding of a semiconductor waferto a substrate.

In many areas of manufacturing, parts to be worked on (processed) mustbe temporarily attached to another work piece or a support. For example,in the manufacture of semiconductor devices it is often necessary tosupport semiconductor wafers for various manufacturing steps. Therequirement for thinner die packages has driven semiconductormanufacturers to thin semiconductor wafers. Such thinning is typicallyaccomplished by temporarily adhering the front side of a semiconductorwafer, which contains active devices, to a carrier (support) in order toallow for grinding of the backside of the wafer. Also, thinned wafersmay be subject to further manufacturing operations, such asmetallization, cleaning, etching, and the like. After such processing,the thinned wafer must be detached (debonded) from the carrier. If thetemporary adhesive bonds too strongly to the wafer, the wafer may sufferdamage, such as breakage, or deformation of bonding features, duringseparation from the carrier. Alternatively, the temporary adhesive maylack sufficient bulk strength and remain on both the active surface(front side) of the wafer and on the substrate after separationrequiring additional cleaning or etching steps.

Conventional temporary bonding adhesives used in the manufacture ofsemiconductor devices are either thermoplastic adhesives or crosslinkingadhesives. Thermoplastic adhesives have the advantage that residualadhesive can be easily removed by solvent cleaning. A major problem withthermoplastic adhesives is that they become soft when heated whichlimits their use in certain applications. Crosslinking adhesives are noteasily removed by solvent cleaning and are typically removed by peelingeither during or after the debonding operation. This peeling steprequires the crosslinking adhesives to have some degree of softness atroom temperature. Unfortunately, this room temperature softness isproblematic as it provides challenges in achieving uniform waferthicknesses after a grinding operation.

In order to address these problems, multilayer approaches have beensuggested where a release layer, such as a silicone material, is firstapplied to the active side of a wafer and then an adhesive is used tobond a substrate to the release layer-wafer. In such a system, a widerrange of adhesives can be used because the ability to debond the waferis provided by the release layer. For example, U.S. Pat. App. Pub. No.2009/0176349 discloses applying a silicone oil to the wafer surface, andthen depositing a graded plasmapolymeric layer followed by a substrate.The plasmapolymeric layer is deposited using a low-pressure plasmapolymerization process where a graded composition of the polymeric layeris achieved by changing the reaction parameters, for example, thereaction gas composition. This process has certain drawbacks: itrequires the application of a separate release layer on the wafer; itrequires a low-pressure plasma polymerization apparatus; and thecomposition of the plasmapolymeric layer that is deposited on the wafermust be selected such that the plasmapolymeric layer has sufficientadhesiveness to the substrate, which may limit the plasma-polymerizablemonomers that may be used.

Accordingly, there remains a need in the industry for temporaryadhesives that are easy to apply, are easily removable, do not deformthe active side of a wafer, and can be used in higher temperatureoperations than current temporary adhesives. The present inventionaddresses one or more of these deficiencies.

The present invention provides a method of releasably attaching asemiconductor wafer to a carrier substrate comprising: (a) providing asemiconductor wafer having a front side and a back side; (b) providing acarrier substrate having an attachment surface; (c) disposing atemporary bonding composition comprising a curable adhesive material anda release additive between the front side of the semiconductor wafer andthe attachment surface of the carrier substrate; and (d) curing theadhesive material to provide a temporary bonding layer disposed betweenthe front side of the semiconductor wafer and the attachment surface ofthe carrier substrate; wherein the temporary bonding layer adjacent tothe attachment surface of the carrier substrate comprises a relativelylower amount of the release additive and the temporary bonding layeradjacent to the front side of the semiconductor wafer comprises arelatively higher amount of the release additive.

Also provided by the present invention is a structure comprising: asemiconductor wafer having a front side and a back side; a carriersubstrate having an attachment surface; and a temporary bonding layerdisposed between the front side of the semiconductor wafer and theattachment surface of the carrier substrate; wherein the temporarybonding layer comprises a cured adhesive material and a releaseadditive; wherein the temporary bonding layer adjacent to the attachmentsurface of the carrier substrate comprises a relatively lower amount ofthe release additive and the temporary bonding layer adjacent to thefront side of the semiconductor wafer comprises a relatively higheramount of the release additive.

Further, the present invention provides a composition comprising acurable adhesive material and a release additive. Preferably, theadhesive material is chosen from polyarylene oligomers, cyclic-olefinoligomers, arylcyclobutene oligomers, and mixtures thereof. The releaseadditive is non-curable under the conditions employed to cure theadhesive material.

It has been surprisingly found that the present invention addresses oneor more of the deficiencies in conventional temporary bonding approachesused in the semiconductor industry. The present invention is effectivein temporarily bonding a semiconductive wafer to a substrate (carrier)during certain processing steps. The wafer is then debonded from thesubstrate with reduced to no deformation of features, and reduced to noresidual adhesive remaining on the active side of the wafer as comparedto conventional temporary bonding adhesives. The present invention isparticularly suitable for use in the processing of semiconductor wafers,or in any other application where a temporary bond is required.

FIGS. 1A-1C are schematic diagrams illustrating alternate aspects of theprocess of the invention.

FIGS. 2A-2F are schematic diagrams illustrating the process of theinvention.

FIGS. 3A-3D are scanning electron micrographs showing the releasabilityof the adhesive of the invention from surfaces containing copperpillars.

FIGS. 4A-4D are scanning electron micrographs showing the releasabilityof the adhesive of the invention from surfaces containing solder bumps.

In the above figures, like numerals refer to like elements. It will beunderstood that when an element is referred to as being “adjacent to”another element, it can be directly adjacent to the other element orintervening elements may be present therebetween. In contrast, when anelement is referred to as being “directly adjacent to” another element,there are no intervening elements present. As used herein, the term“and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that although the terms first, second, third, etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of the present invention.

As used throughout this specification, the following abbreviations shallhave the following meanings, unless the context clearly indicatesotherwise: ° C.=degrees Celsius; g=grams; mg=milligrams; L=liter;ppm=parts per million; μm=micron=micrometers; nm=nanometers;mm=millimeters; mL=milliliters; kPa=kilopascals; and GPa=gigapascals.All amounts are percent by weight and all ratios are molar ratios,unless otherwise noted. All numerical ranges are inclusive andcombinable in any order, except where it is clear that such numericalranges are constrained to add up to 100%. The articles “a” and “an”refer to the singular and the plural. “Wt %” refers to percent byweight, based on the total weight of a referenced composition, unlessotherwise noted.

As used throughout the specification, “feature” refers to the geometrieson a substrate, and particularly on a semiconductive wafer. The term“alkyl” includes linear, branched and cyclic alkyl. Likewise, “alkenyl”refers to linear, branched and cyclic alkenyl. “Aryl” refers to aromaticcarbocycles and aromatic heterocycles. By the term “curing” is meant anyprocess, such as polymerization or condensation, that increases themolecular weight of a material or composition. “Curable” refers to anymaterial capable of being cured (polymerized) under certain conditions.The term “oligomer” refers to dimers, trimers, tetramers and otherrelatively low molecular weight materials that are capable of furthercuring. The articles “a” and “an” refer to the singular and the plural.

It has been found that an adhesive composition comprising a curableadhesive material and a release additive may be used to form anephemeral (or temporary) bonding layer. In use, the present adhesivecomposition is first disposed between a substrate (carrier) surface anda surface of a component, the composition is then cured, and variousoperations may then be performed on the component, after which thecomponent is separated from the substrate.

In particular, the present invention provides a method of releasablyattaching a semiconductor wafer to a carrier substrate comprising: (a)providing a semiconductor wafer having a front side and a back side; (b)providing a carrier substrate having an attachment surface; (c)disposing a temporary bonding composition comprising a curable adhesivematerial and a release additive between the front side of thesemiconductor wafer and the attachment surface of the carrier substrate;and (d) curing the adhesive material to provide a temporary bondinglayer disposed between the front side of the semiconductor wafer and theattachment surface of the carrier substrate; wherein the temporarybonding layer adjacent to the attachment surface of the carriersubstrate comprises a relatively lower amount of the release additiveand the temporary bonding layer adjacent to the front side of thesemiconductor wafer comprises a relatively higher amount of the releaseadditive.

A wide variety of semiconductor wafers may be employed in the presentinvention. As used herein, the term “semiconductor wafer” is intended toencompass “an electronic device substrate,” “a semiconductor substrate,”“a semiconductor device,” and various packages for various levels ofinterconnection, including a single-chip wafer, multiple-chip wafer,packages for various levels, substrates for light emitting diodes(LEDs), or other assemblies requiring solder connections. Particularlysuitable substrates are glass, sapphire, silicate materials, siliconnitride materials, silicon carbide materials, and patterned wafers, suchas patterned silicon wafers and patterned gallium-arsenide wafers. Suchwafers may be any suitable size. Preferred wafer diameters are 200 mm to300 mm, although wafers having smaller and larger diameters may besuitably employed according to the present invention. As used herein,the term “semiconductive substrates” includes any substrate having oneor more semiconductor layers or structures which include active oroperable portions of semiconductor devices. The term “semiconductorsubstrate” is defined to mean any construction comprising semiconductivematerial, including but not limited to bulk semiconductive material suchas a semiconductive wafer, either alone or in assemblies comprisingother materials thereon, and semiconductive material layers, eitheralone or in assemblies comprising other materials. A semiconductordevice refers to a semiconductor substrate upon which at least onemicroelectronic device has been or is being fabricated.

The front side of a semiconductor wafer typically contains “active”devices. An “active” device is any type of circuit component with theability to electrically control electron flow, such as, for example,transistors. Typically, the front side of a semiconductor wafer alsoincludes various features, such as metal bond pads, solder bumps (orsolder balls), metal pillars, and the like. Metal bond pads typicallycomprise one or more metals chosen from copper, tin, gold, and silver.Exemplary solder bumps typically comprise one or more of tin, copper,silver, gold, lead, and bismuth, preferably tin, copper, silver, gold,and lead, and more preferably tin, copper, silver, gold, tin-lead,tin-silver, and tin-silver-copper. Metal pillars typically comprisecopper, often capped with one or more other metals, such as silver ortin-silver. Preferably, the active surface of the semiconductor wafer isrelatively hydrophilic as compared to the attachment surface of thecarrier substrate. The hydrophilicity of the active surface may beincreased by liquid or plasma treatment of the wafer surface to removesurface impurities such as adventitious carbon.

Any suitable carrier may be used as the carrier substrate. Exemplarycarrier substrates include, without limitation, wafers, glass such asborosilicate, quartz, silica, and thermally stable polymers. Wafers usedas carriers may be composed of silicon, silicon carbide, silicongermanium, silicon nitride, gallium arsenide, sapphire, and the like.Thermally stable polymers include, without limitation, any polymerstable to the temperatures used to cure the adhesive material, such aspolyimide (for example, KAPTON™ polyimide, available from DuPont,Wilmington, Del.). Preferably, the attachment surface of the carriersubstrate is relatively hydrophobic as compared to the active surface ofthe semiconductor wafer. If the attachment surface of the carriersubstrate is insufficiently hydrophobic, the desired hydrophobicity maybe imparted by any number of ways known in the art such as by contactingthe attachment surface with a suitable adhesion promoter or by vaportreating the attachment surface. The attachment surface may be contactedwith an adhesion promoter using any suitable method, such asspin-coating, dip coating, spray coating, curtain coating, roll coating,vapor deposition, and the like, and preferably by spin-coating. Variousvapor treatments may be used to increase the hydrophobicity of theattachment surface, such as plasma treatments. Preferably, an adhesionpromoter is used to treat the attachment surface to impart the desiredhydrophobicity. Any suitable adhesion promoter may be used and theselection of such adhesion promoter is well within the ability of thoseskilled in the art. Preferred adhesion promoters are silane-containingmaterials, and more preferably trialkoxysilane-containing materials.Exemplary adhesion promoters include, but are not limited to:bis(trialkoxysilylalkyl)benzenes such asbis(trimethoxysilylethyl)benzene; aminoalkyl trialkoxy silanes such asaminopropyl trimethoxy silane, aminopropyl triethoxy silane, and phenylaminopropyl triethoxy silane; and other silane coupling agents, as wellas mixtures of the foregoing. Particularly suitable adhesion promotersinclude AP 3000 and AP 8000, available from Dow Electronic Materials(Marlborough, Mass.).

The present temporary bonding compositions comprise a curable adhesivematerial and a release additive, and optionally an organic solvent.Typically, the curable adhesive material has a modulus of >1 GPa whencured. Exemplary curable adhesive materials include, without limitation,polyarylene oligomers, cyclic-olefin oligomers, arylcyclobuteneoligomers, and mixtures thereof. The curable adhesive material may besubstituted with any suitable moiety to provide additionalhydrophobicity, such as fluorine-containing groups, as long as suchmoieties do not adversely impact the mechanical properties of the curedadhesive material. Preferably, the curable adhesive material is chosenfrom polyarylene oligomers, cyclic-olefin oligomers, arylcyclobuteneoligomers, and mixtures thereof, and more preferably is one or morearylcyclobutene oligomers.

A wide variety of polyarylene oligomers may be used in the presentinvention. As used herein, the term “polyarylenes” includes polyaryleneethers. Suitable polyarylene oligomers may be synthesized fromprecursors such as ethynyl aromatic compounds of the formula:

wherein each Ar is an aromatic group or inertly-substituted aromaticgroup: each R is independently hydrogen, an alkyl, aryl orinertly-substituted alkyl or aryl group; L is a covalent bond or a groupwhich links one Ar to at least one other Ar; n and m are integers of atleast 2; and q is an integer of at least 1. As such, the ethynylaromatic compounds typically have four or more ethynyl groups (forexample, tetraethynyl aromatic compounds).

Suitable polyarylene oligomers used in the temporary bondingcompositions may comprise a polymer comprising as polymerized units:

wherein Ar′ is the residual of the reaction of product of (C≡C)_(n)—Aror Ar—(C≡C)_(m) moieties and R, L, n and m are as defined above.Polyarylene copolymers useful in the invention include as polymerizedunits a monomer having the formula:

wherein Ar′ and R are as defined above.

Exemplary polyarylenes include, but are not limited to, those whereinAr-L-Ar is: biphenyl; 2,2-diphenyl propane; 9,9′-diphenyl fluorene;2,2-diphenyl hexafluoro propane; diphenyl sulfide; oxydiphenylene;diphenyl ether; bis(phenylene)diphenylsilane; bis(phenylene)phosphineoxide; bis(phenylene)benzene; bis(phenylene)naphthalene;bis(phenylene)anthracene; thiodiphenylene; 1,1,1-triphenyleneethane;1,3,5-triphenylenebenzene; 1,3,5-(2-phenylene-2-propyl)benzene;1,1,1-triphenylenemethane; 1,1,2,2-tetraphenylene-1,2-diphenylethane;bis(1,1-diphenyleneethyl)benzene;2,2′-diphenylene-1,1,1,3,3,3-hexafluoropropane;1,1-diphenylene-1-phenylethane; naphthalene; anthracene; orbis(phenylene)naphthacene; more preferably biphenylene; naphthylene;p,p′-(2,2-diphenylene propane) (or —C₆H₄—C(CH₃)₂—C₆H₄—);p,p′-(2,2-diphenylene-1,1,1,3,3,3hexafluoropropene) and(—C₆H₄—C(CF₃)₂—C₆H₄—). Useful bis-phenyl derivatives include2,2-diphenyl propane; 9,9′-diphenyl fluorene; 2,2-diphenyl hexafluoropropane; diphenyl sulfide; diphenyl ether; bis(phenylene)diphenylsilane;bis(phenylene)phosphine oxide; bis(phenylene)benzene;bis(phenylene)naphthalene; bis(phenylene)anthracene; orbis(phenylene)naphthacene.

The polyarylene precursor monomers may be prepared by a variety ofmethods known in the art, such as by: (a) selectively halogenating,preferably brominating, a polyphenol (preferably a bisphenol) preferablyin a solvent, where each phenolic ring is halogenated with one halogenon one of the two positions ortho to the phenolic hydroxyl group; (b)converting the phenolic hydroxyl on the resultingpoly(ortho-halophenol), preferably in a solvent, to a leaving group suchas a sulfonate ester (for example, a trifluoromethanesulfonate esterprepared from trifluoromethanesulfonyl halide or trifluoromethanesulfonic acid anhydride) which is reactive with and replaced by terminalethynyl compounds; and (c) reacting the reaction product of step (b)with an ethynyl-containing compound or an ethynyl synthon in thepresence of an aryl ethynylation, preferably palladium, catalyst and anacid acceptor to simultaneously replace the halogen and thetrifluoromethylsulfonate with an ethynyl-containing group (for example,acetylene, phenylacetylene, substituted phenylacetylene or substitutedacetylene). Further explanation of this synthesis is provided in Int.Pat. App. No. WO 97/10193 (Babb).

The ethynyl aromatic monomers of Formula (I) are useful to preparepolymers of either Formula (II) or (III). Polymerization of the ethynylaromatic monomers is well within the ability of one skilled in the art.While the specific conditions of polymerization are dependent on avariety of factors including the specific ethynyl aromatic monomer(s)being polymerized and the desired properties of the resulting polymer,the general conditions of polymerization are detailed in Int. Pat. App.No. WO 97/10193 (Babb).

Particularly suitable polyarylenes for use in the present inventioninclude those sold as SiLK™ Semiconductor Dielectric (available from DowElectronic Materials, Marlborough, Mass.). Other particularly suitablepolyarylenes include those disclosed in WO 00/31183, WO 98/11149, WO97/10193, WO 91/09081, EP 755 957, and U.S. Pat. Nos. 5,115,082;5,155,175; 5,179,188; 5,874,516; and 6,093,636.

Suitable cyclic-olefin materials are poly(cyclic-olefins), which may bethermoplastic, and preferably have a weight average molecular weight(M_(w)) of from 2000 to 200,000 Daltons, more preferably from 5000 to100,000 Daltons, and even more preferably from 2000 to 50,000 Daltons.Preferred poly(cyclic-olefins) have a softening temperature (meltviscosity at 3,000 PaS) of at least 100° C., and more preferably atleast 140° C. Suitable poly(cyclic-olefins) also preferably have a glasstransition temperature (T_(g)) of at least 60° C., more preferably from60 to 200° C., and most preferably from 75 to 160° C.

Preferred poly(cyclic-olefins) are comprised of recurring monomers ofcyclic-olefins and acyclic olefins, or ring-opening polymers based oncyclic-olefins. Suitable cyclic olefins for use in the present inventionare chosen from norbornene-based olefins, tetracyclododecene-basedolefins, dicyclopentadiene-based olefins, and derivatives thereof.Derivatives include alkyl (preferably C₁-C₂₀ alkyls, more preferablyC₁-C₁₀ alkyls), alkylidene (preferably C₁-C₂₀ alkylidenes, morepreferably C₁-C₁₀ alkylidenes), aralkyl (preferably C₆-C₃₀ aralkyls,more preferably C₆-C₁₈ aralkyls), cycloalkyl (preferably C₃-C₃₀cycloalkyls, more preferably C₃-C₁₈ cycloalkyls), ether, acetyl,aromatic, ester, hydroxy, alkoxy, cyano, amide, imide, andsilyl-substituted derivatives. Particularly preferred cyclic-olefins foruse in the present invention include those chosen from

and combinations of the foregoing, where each R¹ and R² is independentlychosen from H, and alkyl groups (preferably C₁-C₂₀ alkyls, morepreferably C₁-C₁₀ alkyls), and each R³ is independently chosen from H,substituted and unsubstituted aryl groups (preferably C₆-C₁₈ aryls),alkyl groups (preferably C₁-C₂₀ alkyls, more preferably C₁-C₁₀ alkyls),cycloalkyl groups (preferably C₃-C₃₀ cycloalkyl groups, more preferablyC₃-C₁₈ cycloalkyl groups), aralkyl groups (preferably C₆-C₃₀ aralkyls,more preferably C₆-C₁₈ aralkyl groups such as benzyl, phenethyl,phenylpropyl, and the like), ester groups, ether groups, acetyl groups,alcohols (preferably C₁-C₁₀ alcohols), aldehyde groups, ketones,nitriles, and combinations thereof.

Preferred acyclic olefins are chosen from branched and unbranched C₂-C₂₀alkenes (preferably C₂-C₁₀ alkenes). More preferably, the acyclicolefins have the structure (R⁴)₂C═C(R⁴)₂, where each R⁴ is independentlychosen from H and alkyl groups (preferably C₁-C₂₀ alkyls, morepreferably C₁-C₁₀ alkyls). Particularly preferred acyclic olefins foruse in the present invention include those chosen from ethene, propene,and butene, with ethene being the most preferred.

Methods of producing cyclic-olefin copolymers are known in the art. Forexample, cyclic-olefin copolymers can be produced by chainpolymerization of a cyclic monomer with an acyclic monomer. Whennorbornene is reacted with ethene under such conditions, anethene-norbornene copolymer containing alternating norbornanediyl andethylene units is obtained. Examples of copolymers produced by thismethod include those available under the TOPAS™ (produced by TopasAdvanced Polymers) and APEL™ (produced by Mitsui Chemicals) brands. Asuitable method for making these copolymers is disclosed in U.S. Pat.No. 6,008,298. Cycloolefin copolymers can also be produced byring-opening metathesis polymerization of various cyclic monomersfollowed by hydrogenation. The polymers resulting from this type ofpolymerization can be thought of conceptually as a copolymer of etheneand a cyclic-olefin monomer (such as alternating units of ethylene andcyclopentane-1,3-diyl). Examples of copolymers produced by thisring-opening method include those provided under the ZEONOR™ (from ZeonChemicals) and ARTON™ (from JSR Corporation) brands. A suitable methodof making these copolymers by this ring-opening method is disclosed inU.S. Pat. No. 5,191,026.

Arylcyclobutene oligomers useful as the present curable adhesivematerials are well-known in the art. Suitable arylcyclobutene oligomersinclude, but are not limited to, those having the formula:

wherein B is an n-valent linking group; Ar is a polyvalent aryl groupand the carbon atoms of the cyclobutene ring are bonded to adjacentcarbon atoms on the same aromatic ring of Ar; m is an integer of 1 ormore; n is an integer of 1 or more; and R⁵ is a monovalent group.Preferably, the polyvalent aryl group, Ar, may be composed of 1-3aromatic carbocyclic or heteroaromatic rings. It is preferred that thearyl group comprise a single aromatic ring, and more preferably a phenylring. The aryl group is optionally substituted with 1 to 3 groups chosenfrom (C₁-C₆)alkyl, tri(C₁-C₆)alkylsilyl, (C₁-C₆)alkoxy, and halo,preferably with one or more of (C₁-C₆)alkyl, tri(C₁-C₃)alkylsilyl,(C₁-C₃)alkoxy, and chloro, and more preferably with one or more of(C₁-C₃)alkyl, tri(C₁-C₃)alkylsilyl, and (C₁-C₃)alkoxy. It is preferredthat the aryl group is unsubstituted. It is preferred that n=1 or 2, andmore preferably n=1. It is preferred that m=1-4, more preferably m=2-4,and yet more preferably m=2. Preferably, R⁵ is chosen from H and(C₁-C₆)alkyl, and more preferably from H and (C₁-C₃)alkyl. Preferably, Bcomprises one or more carbon-carbon double bonds (ethylenicunsaturation). Suitable single valent B groups preferably have theformula —[C(R¹⁰)═CR¹¹]_(x)Z, wherein R¹⁰ and R¹¹ are independentlychosen from hydrogen, (C₁-C₆)alkyl, and aryl; Z is chosen from hydrogen,(C₁-C₆)alkyl, aryl, siloxanyl, —CO₂R¹²; each R¹² is independently chosenfrom H, (C₁-C₆)alkyl, aryl, aralkyl, and alkaryl; and x=1 or 2.Preferably, R¹⁰ and R¹¹ are independently chosen from H, (C₁-C₃)alkyl,and aryl, and more preferably H and (C₁-C₃)alkyl. It is preferred thatR¹² is (C₁-C₃)alkyl, aryl, and aralkyl. Z is preferably siloxyl.Preferred siloxyl groups have the formula —[Si(R¹³)₂—O]p-Si(R¹³)₂—,wherein each R¹³ is independently chosen from H, (C₁-C₆)alkyl, aryl,aralkyl, and alkaryl; and p is an integer from 1 or more. It ispreferred that R¹³ is chosen from (C₁-C₃)alkyl, aryl, and aralkyl.Suitable aralkyl groups include benzyl, phenethyl and phenylpropyl.

Preferably, the arylcyclobutene oligomers comprise one or more oligomersof the formula:

wherein each R⁶ is independently chosen from H and (C₁-C₆)alkyl, andpreferably from H and (C₁-C₃)alkyl; each R⁷ is independently chosen from(C₁-C₆)alkyl, tri(C₁-C₆)alkylsilyl, (C₁-C₆)alkoxy, and halo; each R⁸ isindependently a divalent, ethylenically unsaturated organic group; eachR⁹ is independently chosen from H, (C₁-C₆)alkyl, aralkyl and phenyl; pis an integer from 1 or more; and q is an integer from 0-3. Each R⁶ ispreferably independently chosen from H and (C₁-C₃)alkyl, and morepreferably each R⁶ is H. It is preferred that each R⁷ is independentlychosen from (C₁-C₆)alkyl, tri(C₁-C₃)alkylsilyl, (C₁-C₃)alkoxy, andchloro, and more preferably from (C₁-C₃)alkyl, tri(C₁-C₃)alkylsilyl, and(C₁-C₃)alkoxy. Preferably, each R⁸ is independently chosen from a(C₂-C₆)alkenyl, and more preferably each R⁸ is —CH═CH—. Each R⁹ ispreferably chosen from (C₁-C₃)alkyl, and more preferably each R⁹ ismethyl. Preferably, p=1-5, more preferably p=1-3, and yet morepreferably p=1. It is preferred that q=0. A particularly preferredarylcyclobutene oligomer, 1,3-bis(2-bicyclo[4.2.0]octa-1,3,5-trien-3-ylethenyl)-1,1,3,3tetramethyldisiloxane (“DVS-bisBCB”), has the formula

Arylcyclobutene oligomers may be prepared by any suitable means, such asthose described in U.S. Pat. Nos. 4,812,588; 5,136,069; 5,138,081; andInternational Pat. App. No. WO 94/25903. Suitable arylcyclobuteneoligomers are also commercially available under the CYCLOTENE™ brand,available from Dow Electronic Materials. The arylcyclobutene oligomersmay be used as is, or may be further purified by any suitable means.

A wide variety of materials may be used as the release additives in thetemporary bonding compositions provided that such materials do not reactwith the adhesive material under conditions of storage and use, and arenon-curable under the conditions used to cure the adhesive material. Inaddition, the release additives should be compatible with the temporarybonding composition, that is, the release additives must be dispersible,miscible or otherwise substantially compatible with the adhesivematerial, and any other components, such as organic solvents, used inthe temporary bonding composition. When an organic solvent (or mixedsolvent system) is used in the temporary bonding composition, both therelease additive and the curable adhesive material must be soluble insuch solvent. The present release additives are sufficientlynon-volatile such that they do not substantially evaporate under theconditions of use, that is, they substantially do not evaporate duringany deposition step, such as spin-coating, or any subsequent heatingstep used to remove any organic solvent or to cure the adhesivematerial. When a film or layer of the temporary bonding composition iscast, such as by spin-coating, much (or all) of the solvent evaporates.It is preferred that the release additive is soluble in any organicsolvent used, but is not completely soluble in the curable adhesivematerial. The release additives are preferentially more hydrophilic thanthe cured adhesive material. Not being bound by theory, it is believedthat upon curing of the adhesive material, the release additive phaseseparates and migrates preferentially toward the active surface of thewafer (the more hydrophylic surface as compared to the carrier surface).The use of appropriate hydrophilic moieties in the release additivesallow for complete dispersion, or preferably dissolution, of the releaseadditive in the temporary bonding composition, and phase separation ofthe release additive during curing of the adhesive material withmigration of the release additive toward the more hydrophilic surface.

In general, the release additives will contain one or more relativelyhydrophilic moieties, such as moieties containing one or more of oxygen,nitrogen and sulfur. Suitable release additives include, withoutlimitation: ethers, esters, carboxylates, alcohols, thioethers, thiols,amines, imines, amides, and mixtures thereof. Preferably, the releaseadditives contain one or more polar end groups, which contain one ormore of oxygen, nitrogen and sulfur, and preferably oxygen. Exemplarypolar end groups include: alkoxy, aryloxy, hydroxy, carboxylate,alkoxycarbonyl, mercapto, alkylthio, primary amine, secondary amine, andtertiary amine; preferably the end groups are chosen from (C₁-C₆)alkoxy,(C₆-C₁₀)aryloxy, hydroxy, carboxylate, (C₁-C₆)alkoxycarbonyl, mercapto,(C₁-C₆)alkylthio, amino, (C₁-C₆)alkylamino, and di(C₁-C₆)alkylamino;more preferably from (C₁-C₆)alkoxy, (C₆-C₁₀)aryloxy, hydroxy,carboxylate, and (C₁-C₆)alkoxycarbonyl; and even more preferably from(C₁-C₆)alkoxy, hydroxy, carboxylate, and (C₁-C₆)alkoxycarbonyl.Particularly preferred polar end groups are chosen from hydroxy,methoxy, ethoxy, propoxy, butoxy, carboxyl, and acetoxy.

Suitable release additives have a weight average molecular weight(M_(w)) of ≦10,000 Daltons, preferably ≦7500 Daltons, and morepreferably ≦5000 Daltons. The release additives have a minimum molecularweight (M_(w)) sufficient to render the release additives substantiallynon-volatile during conditions of use, that is, <5%, preferably <3%, andmore preferably ≦1% of the release additive is volatilized during use.Preferably, the release additives have a M_(w) of ≧500 Daltons. Apreferred range of M_(w) is from 500 to 10,000 Daltons, more preferablyfrom 500 to 7500 Daltons, and yet more preferably from 500 to 7000Daltons. While the release additives may be linear polymers; branchedpolymers such as dendritic polymers, star polymers, and the like;polymer particles; and the like, it is preferred that the releaseadditives are linear polymers or polymer particles, and more preferablylinear polymers. While not being bound by theory, it is believed thatlinear polymers are better able to migrate through the curing adhesivematerial phase toward the hydrophilic wafer surface as compared tobranched polymers.

Polyethers are the preferred release additives. Polyether compoundsinclude alkyleneoxide homopolymers and alkyleneoxide copolymers.Polyalkylene oxide release additives may have a variety of polar endgroups, preferably such polar end groups are hydroxy, (C₁-C₆)alkoxy, and(C₁-C₆)alkoxycarbonyl, and more preferably hydroxy, (C₁-C₃)alkoxy, andacetoxy. Preferred polyether compounds include polyethylene glycol,polypropyleneglycol, poly(1,3-propanediol), polybutyleneglycol,poly(tetrahydrofuran), ethylene glycol-propylene glycol copolymers, andmixtures thereof. It will be appreciate by those skilled in the art thatmixtures of release additives may be used in the present temporarybonding compositions. Suitable release additives include polyethers soldunder the PLURONIC, TETRONIC and POLYTHF product names (available fromBASF, Ludwigshafen, Germany), the FORTEGRA product name (available fromThe Dow Chemical Company, Midland Mich.), and the TERATHANE product name(available from Invista, Wichita, Kans.), all of which may be usedwithout further purification.

It is preferred that one or more organic solvents be used in thetemporary bonding composition. Any solvent or mixture of solvents thatdissolves or disperses, and preferably dissolves, the curable adhesivematerial and release additive may suitably be used in the temporarybonding compositions. Exemplary organic solvents include, withoutlimitation: aromatic hydrocarbons such as toluene, xylene, andmesitylene; alcohols such as 2-methyl-1-butanol, 4-methyl-2-pentanol,and methyl isobutyl carbinol; esters such as ethyl lactate, propyleneglycol methyl ether acetate, and methyl 2-hydroxyisobutyrate; lactonessuch as gamma-butyrolactone; lactams such as N-methylpyrrolidinone;ethers such as propylene glycol methyl ether and dipropylene glycoldimethyl ether isomers (commercially available from The Dow ChemicalCompany as PROGLYDE™ DMM); ketones such as cyclohexanone andmethylcyclohexanone; and mixtures thereof.

The present temporary bonding compositions may optionally include one ormore additional components, such as curing agents. Suitable curingagents may aid in the curing of the adhesive material, and may beactivated by heat or light. Exemplary curing agents include, but are notlimited to, thermally generated initiators, photoinitiators, azides,nitrenes, and crosslinking agents such as polyamines and polythiols. Theselection of such curing agents is well within the ability of thoseskilled in the art.

The temporary bonding composition comprises one or more curable adhesivematerials in an amount of 50 to 99 wt %, one or more release additivesin an amount of 1 to 50 wt %, optionally organic solvent, and optionallyone or more additional components. The curable adhesive material ispreferably present in an amount of 50 to 95 wt %. It is preferred thatthe release additive is present in an amount of 2 to 50, more preferablyfrom 5 to 45, and even more preferably from 5 to 40 wt %. When present,the amount of organic solvent is preferably sufficient to dissolve ordisperse, and preferably dissolve, the curable adhesive material and therelease additive. The amount of organic solvent is typically from 0 to50 wt %. Preferably, an organic solvent is used. The present temporarybonding compositions may be prepared by combining the curable adhesivematerial, the release additive, and any optional components in anyorder.

In use, the present temporary bonding compositions may be disposed byany suitable method on the attachment surface of the carrier substrate,the front side of the semiconductor wafer, or on both surfaces. Suitablemethods for disposing the temporary bonding composition include, but arenot limited to, spin-coating, curtain coating, spray coating, rollercoating, dip coating, vapor deposition, and lamination such as vacuumlamination, among other methods. In the semiconductor manufacturingindustry, spin-coating is a preferred method to take advantage ofexisting equipment and processes. In spin-coating, the solids content ofthe composition may be adjusted, along with the spin speed, to achieve adesired thickness of the composition on the surface it is applied to.Typically, the present compositions are spin-coated at a spin speed of400 to 4000 rpm. The amount of the temporary bonding compositiondispensed on the wafer or substrate depends on the total solids contentin the composition, the desired thickness of the resulting temporarybonding layer, and other factors well-known to those skilled in the art.Preferably, after being disposed on a surface, the temporary bondingcomposition is heated (baked) to remove any solvent present. Typicalbaking temperatures are from 90 to 140° C., although other temperaturesmay be suitably used. Such baking to remove residual solvent istypically done for approximately 2 minutes, although longer or shortertimes may suitably be used.

In an alternate preferred method, the temporary bonding composition isformed as a dry film and is disposed on the attachment surface of thecarrier substrate, the front side of the semiconductor wafer, or on bothsurfaces by lamination. A variety of suitable lamination techniques,including vacuum lamination techniques, may be used and are well knownto those skilled in the art. In forming a dry film, the temporarybonding composition is first disposed onto a front surface of a suitablefilm support sheet such as a polyester sheet, preferablypolyethyleneterephthalate (PET) sheet, or a polyimide sheet such asKapton™ polyimide, using slot-die coating, gravure printing, or anotherappropriate method. The composition is then soft baked at a temperatureranging from 90 to 140° C. for an appropriate time, such as from 1 to 30minutes, to remove any solvent. A polymer film cover sheet such aspolyethylene is then roll-laminated at room temperature onto the driedtemporary bonding composition to protect the composition during storageand handling. To dispose the dried temporary bonding composition ontothe carrier and/or the semiconductor wafer, the cover sheet is firstremoved. Then, the dried temporary bonding composition on the supportsheet is laminated onto the appropriate surface using roll-lamination orvacuum lamination. The lamination temperature can range from 20 to 120°C. The support sheet is then removed (peeled), leaving the driedtemporary bonding composition on that surface. Using this method, thestructures illustrated in FIGS. 1A, 1B, and 1C can all be realized.

FIG. 1A illustrates a first embodiment of the invention where temporarybonding composition 3 is disposed, such as by spin-coating, on optionaladhesion promoter layer 2 on the attachment surface of carrier substrate1. FIG. 1B illustrates an alternate embodiment of the invention wheretemporary bonding composition 3 is disposed on the front surface ofsemiconductor wafer 5 having features such as metal pillars 4 a and/orsolder bumps 4 b. It will be appreciated by those skilled in the artthat a semiconductor wafer may have only metal pillars, or solder bumps,or a combination of metal pillars and solder bumps, or neither metalpillars nor solder bumps. Temporary bonding composition 3 in FIG. 1B issufficiently flowable to fill-in around features 4 a and 4 b. In FIG.1B, the attachment surface of carrier substrate 1 has optional adhesionpromoter layer 2. FIG. 1C illustrates a third embodiment of theinvention where temporary bonding composition 3 is disposed both on thefront side of semiconductor wafer 5 and on the attachment surface ofcarrier substrate 1 having adhesion promoter layer 2. Temporary bondingcomposition 3 in FIG. 1C is sufficiently flowable to fill-in aroundfeatures 4 a and 4 b. In FIG. 1C, the temporary bonding compositiondisposed on the semiconductor wafer may be the same as, or differentfrom, the temporary bonding disposed on the attachment surface of thecarrier substrate. It will be appreciated by those skilled in the artthat multiple layers of the temporary bonding composition may be appliedin order to achieve the desired thickness.

After the temporary bonding composition is disposed on the front side ofthe semiconductor wafer or the attachment surface of the carriersubstrate, a structure is formed by bringing the attachment surface ofthe carrier wafer or the front surface of the semiconductor wafer,respectively, into contact with the temporary bonding composition, asillustrated by the arrows in FIGS. 1A and 1B. After the temporarybonding composition is disposed on both the front side of thesemiconductor wafer and the attachment surface of the carrier substrate,a structure is formed by bringing the two temporary bonding compositionlayers into contact, as illustrated by the arrow in FIG. 1C. Anysuitable method may be used to bring into contact the carrier substrate,semiconductor wafer and temporary bonding composition, such as bythermocompression bonding, where pressure and heat are applied.Exemplary methods are described in U.S. Pat. No. 7,713,835 and in U.S.Pat. App. Pub. Nos. 2010/0263794 and 2011/0272092. Typically,thermocompression bonding is carried out under vacuum in order to reducevoiding. It is preferred that both the carrier substrate and thesemiconductor wafer are placed in a vacuum chamber, the temporarybonding composition disposed on at least one of the carrier substrateand the wafer is then heated to a desired temperature, such as 50 to200° C. for 1 to 10 minutes in the case of an arylcyclobutene adhesivematerial, next the chamber is evacuated and the carrier substrate andthe semiconductor wafer are contacted to the temporary bondingcomposition, and the chamber is then optionally pressurized, such as to1 to 100 kPa. Next, the bonded pair may be removed from the chamber andcured, or optionally cured within the chamber. Curing of the temporarybonding composition is typically achieved by heating the composition toa temperature of 180 to 250° C. for 1 to 600 minutes in the case of anarylcyclobutene adhesive material.

FIG. 2A illustrates a structure formed after the components illustratedin each of FIGS. 1A-1C are brought into contact. In FIG. 2A,semiconductor wafer 5 has topographic features shown as metal pillars 4a and solder bumps 4 b, temporary bonding composition 3 is directlyadjacent semiconductor wafer 5 and is disposed around features 4 a and 4b, temporary bonding composition is also directly adjacent to optionaladhesion promoter layer 2 which is directly adjacent carrier substrate1. Once the structure in FIG. 2A is formed, the temporary bondingcomposition is then subjected to conditions sufficient to cure theadhesive material. Such conditions include heating, exposure to actinicradiation (light) or a combination thereof. Preferably, heating is used,either alone or in combination with exposure to light, and morepreferably the adhesive material is cured by heating. The rate ofheating is chosen such that the adhesive material does not cureinstantaneously, but cures in a more controlled manner. That is, therate of polymerization must be less than the rate of phase separation.

During curing, without being bound by theory, it is believed that therelease additive phase separates from the curing adhesive material (thatis, polymerization induced phase separation occurs) and generallymigrates toward the relatively more hydrophilic surface (front side) ofthe semiconductor wafer. Following curing, a temporary bonding layer isformed between the semiconductor wafer and the attachment surface of thecarrier substrate as illustrated in FIG. 2B, where the cured temporarybonding composition (now the temporary bonding layer) 3 is composed of afirst region 3 a adjacent to the carrier wafer comprising a relativelylower amount of release additive and a second region 3 b adjacent to thesemiconductor wafer and comprising a relatively higher (greater) amountof release additive. Region 3 b is relatively smaller as compared toregion 3 a. FIG. 2B shows defined regions 3 a and 3 b only for purposesof illustration. It is believed, without being bound by theory, thatregions 3 a and 3 b may represent a continuum of concentrations (fromlower at 3 a to higher at 3 b) of the release additive in the temporarybonding layer or they may represent distinct regions comprisingdifferent concentrations of the release additive, where region 3 b maycomprise a predominant amount of release additive. Whether regions 3 aand 3 b represent distinct regions or a continuum, region 3 bpredominantly comprises the release additive. When the cured adhesivematerial (temporary bonding layer) is composed of an arylcyclobuteneadhesive material, such cured material typically has a modulus of >1GPa, and an elongation of <20% at the breaking point.

Once the temporary bonding layer is formed, one or more suitableoperations may be performed on the semiconductor wafer, such as grinding(thinning) the backside of the wafer, as illustrated in FIG. 2C wherethe backside of semiconductor wafer 5 has been ground (thinned) and aflat surface 5 a formed. Further operations may be performed, such aspatterning, the formation of via holes, and the formation of conductivecontacts on the backside of the semiconductor wafer. FIG. 2D illustratesa structure having carrier substrate 1 having an optional adhesionpromoter layer 2, temporary bonding layer 3 joining semiconductor wafer5 to carrier substrate 1, where the temporary bonding layer surroundsfeatures, such as metal pillars and/or solder bumps on the front side ofthe semiconductor wafer, where the backside of wafer 5 has been groundand metal contacts 6 formed thereon.

The greater concentration of release additive adjacent, and preferablydirectly adjacent, to the front side of the semiconductor wafer relativeto the concentration of the release additive in the temporary bondinglayer adjacent to the carrier substrate provides a structure having alower adhesion energy between the semiconductor wafer and the temporarybonding layer as compared to the adhesion energy between the carriersubstrate and the temporary bonding layer. Preferably, the difference inadhesion energy between the semiconductor wafer-temporary bonding layerinterface and the carrier substrate-temporary bonding layer interfaceis >20 J/m², and more preferably >25 J/m². The temporary bonding layerand the front side of the semiconductor wafer have an adhesion energy of≦5 J/m², preferably <5 J/m², more preferably <3 J/m², and mostpreferably ≦2 J/m². The adhesion energy between the temporary bondinglayer and the attachment surface of the carrier substrate ispreferably >30 J/m², more preferably >35 J/m², and yet more preferably≧40 J/m². Such differences in adhesion energy allows for easier releaseof the semiconductor wafer from the temporary bonding layer as comparedto the carrier substrate.

After completion of the operations to be performed on the semiconductorwafer, the wafer is then separated from the carrier substrate and thetemporary bonding layer. Any suitable method for separating thesemiconductor wafer from the temporary bonding layer may be used, suchas those disclosed in U.S. Pat. App. Pub. Nos. 2010/0263794;2011/0308739; and 2012/0028438, and Int. Pat. App. No. WO 2011/079170.The structure may optionally be heated in order to facilitate separationof the semiconductor wafer, but such heating is not required. Anadvantage of the present invention is that with such low adhesion energybetween the temporary bonding layer and the semiconductor wafer,separation is easily achieved by forcing a wedge between thesemiconductor wafer and the carrier substrate to force or pry apart thestructure. Once separation initiates, the semiconductor wafer is easilyseparated from the temporary bonding layer. FIG. 2E illustrates oneaspect of the invention showing processed semiconductor wafer 5 havingtopographic features shown as metal pillars 4 a and solder bumps 4 b onthe front side and conductive contacts 6 on the back side separatingfrom carrier substrate 1 having optional adhesion promoter layer 2, andboth regions 3 a and 3 b of the temporary bonding layer. The processedsemiconductor wafer 5 is then rinsed with an appropriate solvent orsolvent mixture to remove any residue, and then dried. Suitable rinseagents include, without limitation, isopropanol, acetone, ammonia/water,water/surfactant, and the like. FIG. 2F illustrates an alternate aspectwhere region 3 b remains on the front side of the semiconductive waferfollowing separation, which is then easily removed by contactingsemiconductor wafer 5 with an appropriate solvent or solvent mixturefollowed by drying. As illustrated in FIGS. 2E and 2F, the presenttemporary bonding layer is able to be removed from the surface of asemiconductive wafer, even from areas having topographic features suchas metal pillars and solder bumps, leaving little to no cured adhesivematerial residue.

FIGS. 3A-3D are scanning electron micrographs showing the releasabilityof a semiconductor wafer having an array of copper pillars from thepresent temporary bonding layer comprising DVS-bisBCB as the curableadhesive material and a polyether release additive. FIG. 3A shows thearray of copper pillars on the semiconductor wafer after separation fromthe present temporary bonding layer and solvent rinsing. FIG. 3B isshows the surface of the temporary bonding layer after separation fromthe semiconductor wafer. FIG. 3C is a close-up view of a single copperpillar from the array on the semiconductor wafer and FIG. 3D is aclose-up of a single hole in the temporary bonding layer afterseparation of the semiconductor wafer. As can be seen from thesemicrographs, the semiconductor wafer separated completely from thetemporary bonding layer, with no visible residue remaining on either thewafer surface or on the copper pillars after solvent rinsing, and withlittle to no damage to the semiconductor wafer.

FIGS. 4A-4D are scanning electron micrographs showing the releasabilityof a semiconductor wafer having an array of solder bumps from thepresent temporary bonding layer comprising DVS-bisBCB as the curableadhesive material and a polyether release additive. FIG. 4A shows thearray of solder bumps on the semiconductor wafer after separation fromthe present temporary bonding layer and solvent rinsing. FIG. 4B isshows the surface of the temporary bonding layer after separation fromthe semiconductor wafer. FIG. 4C is a close-up view of a single solderbump from the array on the semiconductor wafer and FIG. 4D is a close-upof a single hole in the temporary bonding layer after separation of thesemiconductor wafer. As can be seen from these micrographs, thesemiconductor wafer separated completely from the temporary bondinglayer, with no visible residue remaining on either the wafer surface oron the solder bumps after solvent rinsing.

Certain topographic features, such as solder bumps, present challengesin removing any temporary bonding layer due to their shape. Accordingly,higher amounts of release additive may be required in the presenttemporary bonding compositions in order to ensure good release of asemiconductor wafer having these topographic features. Higher amounts ofrelease additive will result in a larger region (3 b in FIG. 2B) thatpredominantly comprises the release additive adjacent to the front sideof the semiconductor wafer, which will facilitate separation of thewafer in areas having such topographic features.

The following test methods were used in the following examples.

Semiconductor Wafer Coating:

Silicon wafers were coated on a Brewer CEE 400 spin-coating system withan integrated hot plate and wafer transfer system. An amount (6-8 g) ofa sample was disposed on an untreated silicon wafer using a dynamicdispense and a spin speed of 1000 to 2000 rpm for up to 45 seconds,followed by soft bake at 120° C. for 90 seconds on a hot plate. Thefinal coating thickness was inversely dependent on spin speed and rangedfrom 25 to 50 μm.

Carrier Substrate Coating:

Unless other wise specified, carrier wafers were prepared for thebonding study by treating the wafer surface with a trialkoxysilaneadhesion promoter (AP-3000™ Adhesion Promoter available from DowElectronic Materials) to enhance adhesion of the temporary bonding layerafter cure. The adhesion promoter was applied using a spin-coater with astatic dispense followed by spinning at 2000 rpm for 45 seconds and ahot plate bake step at 90° C. for 90 sec.

Semiconductor Wafer to Carrier Substrate Bonding:

Two silicon wafer pieces, one having a layer of temporary bondingcomposition disposed thereon, were bonded by heating on a hot plateplacing in direct contact and then attaching a clamp to prevent theparts from sliding apart. The samples were then cured in a rapid thermalannealing chamber at 260° C. for 1 hour.

Single Cantilever Beam Adhesion Test:

Parts to be evaluated were attached to a load cell and then thesemiconductor wafer and carrier substrate were separated at a slow rateby applying a wedge open stress, according to the method described in S.Chauffaille, et al., “Pre-Cracking Behaviour in the Single CantileverBeam Adhesion Test,” Int. J. Fract (2011) 169: 133-144.

EXAMPLE 1 Control 1

A composition containing 63 wt % of DVS-bisBCB oligomer (as curableadhesive material) solution in mesitylene (from The Dow ChemicalCompany) was deposited onto a clean silicon wafer by spin-coatingfollowed by a 120° C./10 min soft bake to remove the solvent. On asecond silicon wafer (the carrier substrate), the adhesion promoter wasapplied by spin-coating followed by a 120° C./2 min soft bake to removethe solvent. The two wafers were pressed together at 180° C. for 10minutes followed by a cure at 210° C. for 30 minutes. The bonded waferpair was allowed to cool to room temperature. Upon attempting toseparate the semiconductor wafer from the carrier substrate using awedge-open process, where a wedge such as a razor blade is insertedbetween the wafers and used to pry them apart, it was found that thewafers could not be separate due to the high adhesion energy of thecured adhesive material.

EXAMPLE 2 Control 2

A composition of DVS-bisBCB oligomer (25,000 molecular weight) inmesitylene at 65% solids was spin-coated on a semiconductor wafer andcured. The adhesion of the cured DVS-bisbenzocyclobutene film to thesilicon surface was measured to be 9 J/m² using the single cantileverbeam test method.

EXAMPLE 3 Comparative

To 100 g of 63% DVS-bisBCB oligomer (having a molecular weight of25,000) in mesitylene was added 13.83 g of BAC-45, a diacrylateterminated butadiene rubber having a molecular weight of 3000 togenerate a transparent solution. The solution was filtered through a 0.4μm polytetrafluoroethylene (PTFE) filter. The solution was spin-coatedon a semiconductor wafer and cured. The adhesion of the curedDVS-bisbenzocyclobutene film to the silicon surface was measured to be64.5 J/m² using the single cantilever beam test method. In addition, nophase separation in the cured DVS-bisBCB layer was observed.

EXAMPLE 4

To 100 g of a 63% solid DVS-bisBCB (curable adhesive material) solutionin mesitylene was added 11.18 g (15 wt % based on the total weight ofthe composition) of poly(tetramethylene glycol), having a molecularweight of 2000, (available as POLYTHF 2000, from BASF) as the releaseadditive. Upon mixing, a single phase system formed with no visiblephase separation. The solution was filtered through a 0.4 μm PTFEmembrane. The solution was spin-coated on a semiconductor wafer andcured. The adhesion of the cured DVS-bisbenzocyclobutene film to thesilicon surface was measured to be 1-2 J/m² using the single cantileverbeam test method. The release additive was shown to migrate to thesurface based on the waxy appearance and the easy removal of the curedadhesive material from the silicon wafer.

EXAMPLE 5

The procedure of Example 4 was repeated except that an ethyleneoxide-butylene oxide-ethylene oxide block copolymer was used at 10 wt %.The adhesion of the cured DVS-bisbenzocyclobutene film to the siliconsurface was measured to be <1 J/m² using the single cantilever beam testmethod. The release additive was shown to migrate to the surface basedon the waxy appearance and the easy removal of the cured adhesivematerial from the silicon wafer.

EXAMPLE 6

A composition containing 90 g of a 63 wt % DVS-bisBCB oligomer (curableadhesive material) in mesitylene and 10 g of polyethylene glycol havinga 12,000 molecular weight (from Fluka) as the release additive wasprepared and stirred at 120° C. until a homogenous mixture was obtained.The resulting temporary bonding composition was then cooled to roomtemperature. Next, the temporary bonding composition was deposited ontoa clean silicon wafer (semiconductor wafer) by spin-coating followed bya 120° C./10 min soft bake to remove the solvent. On a second siliconwafer (carrier substrate), the adhesion promoter was applied byspin-coating followed by a 120° C./2 min soft bake. The two wafers werethen pressed together at 180° C. for 10 minutes followed by a cure at210° C. for 30 minutes. The bonded wafer pair is allowed to cool to roomtemperature. Upon the insertion of a sharp razor edge between thewafers, the two wafers were easily separated with the cured temporarybonding layer adhering to the carrier substrate wafer.

EXAMPLE 7

The procedure of Example 6 was repeated except that the followingrelease additives were used. In each case, the amount of the releaseadditive was 10 g (10 wt %). In each case, the two wafers were easilyseparated with the cured temporary bonding layer adhering to the carriersubstrate wafer. In the following table, “EO” refers to ethyleneoxy,“PO” refers to propyleneoxy, and “BO” refers to butyleneoxy. Visualinspection was used to note the presence of any residue remaining on thesurface of the semiconductor wafer after separation from the temporarybonding layer. Such remaining residue is easily removed by rinsing thesemiconductor wafer with an appropriate solvent.

Sample Release Additive Mol. Wt. Residue 7A Poly(propylene glycol) 1000No 7B Poly(tetramethylene glycol) 2000 No 7C EO-PO-EO block copolymer4400 Yes 7D EO-BO-EO block copolymer 7000 No 7E PO-EO-PO block copolymer3100 Yes

EXAMPLE 8

Adhesion to Carrier Substrate and Semiconductor Wafer: The function ofthe release additive is to reduce the adhesion between the curedadhesive material and the semiconductor while sufficient adhesion to thecarrier substrate is maintained. This is shown quantitatively bymeasuring the critical strain energy release rate, G_(C), of therespective interfaces. The method employed was the single cantileverbeam method described above. The critical strain energy release rate,G_(C), is related to load and fracture (P_(C)), the crack length (a),the beam thickness (h), the beam width (B), and the beam plain strainelastic modulus (E′):

$G_{C} = \frac{6a^{2}P_{C}^{2}}{E^{\prime}h^{3}B^{2}}$

The adhesion to an adhesion promoter coated carrier substrate and baresilicon of both pure DVS-BCB and a composition containing 90 wt %DVS-BCB oligomer as the curable adhesive material and 10 wt %poly(tetramethylene glycol) having a molecular weight of 2000 (fromBASF) as the release additive was measured. The measured values arereported in the following table, where “APCS” refers to the adhesionpromoted carrier substrate surface, “SW” refers to the front side of thesemiconductor wafer, and “RA” refers to the release additive.

Interface Adhesion Energy (J/m²) APCS/100% DVS-BCB (Control) 56 APCS/90%DVS-BCB + 10% RA (Invention) 41 SW/100% DVS-BCB (Control) 10 SW90%DVS-BCB + 10% RA (Invention) 2

The poly(tetramethylene glycol) release additive reduces the adhesion ofthe cured composition to silicon by 80%, enabling release of thesemiconductor wafer. Additionally, the adhesion to the adhesion promotedcoated carrier substrate is only reduced by 27%, thus ensuring that thecured composition will adhere to carrier substrate while releasingcleanly from the semiconductor wafer.

EXAMPLE 9

The procedure of Example 4 is repeated except that a tetrafunctionalblock copolymer derived from the sequential addition of propylene oxide(“PO”) and ethylene oxide (“EO”) to ethylene diamine, having an averagemolecular weight of 4700 and a PO:EO ratio of 90:10 (TETRONIC 901,available from BASF), is used as the release additive.

EXAMPLE 10

The procedure of Example 9 is repeated except that a tetrafunctionalblock copolymer derived from the sequential addition of PO and EO toethylene diamine, having an average molecular weight of 4000 and a PO:EOratio of 80:20 (TETRONIC 702, available from BASF), is used as therelease additive in an amount of 20 wt %, based on the total weight ofthe composition.

EXAMPLE 11

The procedure of Example 9 is repeated except that a tetrafunctionalblock copolymer derived from the sequential addition of PO and EO toethylene diamine, having an average molecular weight of 4000 and a PO:EOratio of 60:40 (TETRONIC 304, available from BASF), is used as therelease additive in an amount of 23 wt %, based on the total weight ofthe composition.

EXAMPLE 12

A temporary bonding composition is prepared by combining 6 g of anethene-norbornene copolymer (TOPAS™ 5010, T_(g) 110° C.; available fromTOPAS Advanced Polymers, Florence, Ky.), 35 g of methylcyclohexane, 14 gof a low molecular weight cycloolefin copolymer (TOPAS™ Toner™, M_(w)8000, M_(w)/M_(n) 2.0), and 5 g of poly(tetramethylene glycol) having amolecular weight of 2000 (available as POLYTHF 2000, from BASF) as therelease additive. The solution is allowed to stir at room temperatureuntil the ingredients dissolve. The composition is then used to bond awafer to a carrier substrate according to the procedure of Example 1.

EXAMPLE 13

A temporary bonding composition is prepared by combining 7.5 g of anethene-norbornene copolymer (TOPAS™ 5013, T_(g) 134° C., 40 g ofmethylcyclohexane, 12.5 g of a low molecular weight cycloolefincopolymer (TOPAS™ Toner™, M_(w) 8000, M_(w)/M_(n) 2.0), 0.15 grams of aphenolic antioxidant (IRGANOX™ 1010), and 0.2 grams of a phosphoniteantioxidant (IRGAFOX™ P-EPQ) and 7.5 g of polyethylene glycol having a12,000 molecular weight as the release additive. The solution is allowedto stir at room temperature until the ingredients dissolve. Thecomposition is then used to bond a wafer to a carrier substrateaccording to the procedure of Example 1.

EXAMPLE 14

A temporary bonding composition is prepared by combining 26.4 g of ahydrogenated norbornene-based copolymer prepared by ring-openingpolymerization (ZEONOR™ 1060, T_(g) 100° C.; available from ZeonChemicals, Louisville, Ky.), 21.6 g of a low molecular weightcycloolefin copolymer (TOPAS™ Toner™), 72 g of methylcyclohexane, and 35g of a tetrafunctional block copolymer derived from the sequentialaddition of PO and EO to ethylene diamine, having an average molecularweight of 4000 and a PO:EO ratio of 80:20 (TETRONIC 702), is used as therelease additive. The solution is allowed to stir at room temperatureuntil the ingredients dissolve. The composition is then used to bond awafer to a carrier substrate according to the procedure of Example 1.

What is claimed is:
 1. A method of releasably attaching a semiconductorwafer to a carrier substrate comprising: (a) providing a semiconductorwafer having a front side and a back side; (b) providing a carriersubstrate having an attachment surface; (c) disposing a temporarybonding composition comprising a curable adhesive material and a releaseadditive between the front side of the semiconductor wafer and theattachment surface of the carrier substrate; and (d) curing the adhesivematerial to provide a temporary bonding layer disposed between the frontside of the semiconductor wafer and the attachment surface of thecarrier substrate; wherein the temporary bonding layer adjacent to theattachment surface of the carrier substrate comprises a relatively loweramount of the release additive and the temporary bonding layer adjacentto the front side of the semiconductor wafer comprises a relativelyhigher amount of the release additive.
 2. The method of claim 1 whereinthe curable adhesive material is chosen from polyarylene oligomers,cyclic-olefin oligomers, arylcyclobutene oligomers, and mixturesthereof.
 3. The method of claim 1 wherein the release additive is apolyether compound.
 4. The method of claim 3 wherein the releaseadditive is chosen from polyalkylene oxide homopolymers and polyalkyleneoxide copolymers.
 5. The method of claim 4 wherein the polyethercompound comprises terminal groups chosen from hydroxy, alkoxy, aryloxy,and mixtures thereof.
 6. The method of claim 4 wherein the polyethercompound is chosen from polyethylene glycol, polypropyleneglycol,poly(1,3-propanediol), polybutyleneglycol, poly(tetrahydrofuran),ethylene glycol-propylene glycol copolymers, and mixtures thereof. 7.The method of claim 1 wherein the temporary bonding composition is curedby the use of heat, light, radiation, or a mixture thereof.
 8. Themethod of claim 1 further comprising the step of treating the attachmentsurface of the carrier substrate with an adhesion promoter prior tocontact with the temporary bonding composition.
 9. The method of claim 1further comprising the steps of: (e) performing an operation on the backside of the semiconductor wafer; and (f) separating the front side ofthe semiconductor wafer from the temporary bonding layer.
 10. The methodof claim 1 wherein the temporary bonding composition further comprisesan organic solvent.
 11. A structure comprising: a semiconductor waferhaving a front side and a back side; a carrier substrate having anattachment surface; and a temporary bonding layer disposed between thefront side of the semiconductor wafer and the attachment surface of thecarrier substrate; wherein the temporary bonding layer comprises a curedadhesive material and a release additive; wherein the temporary bondinglayer adjacent to the attachment surface of the carrier substratecomprises a relatively lower amount of the release additive and thetemporary bonding layer adjacent to the front side of the semiconductorwafer comprises a relatively higher amount of the release additive. 12.The structure of claim 11 further comprising an adhesion promoting layerdisposed between the temporary bonding layer and the attachment surfaceof the carrier substrate.
 13. The structure of claim 11 wherein thetemporary bonding layer and the front side of the semiconductor waferhave an adhesion energy of <3 J/m².
 14. The structure of claim 11wherein the temporary bonding layer and the attachment surface of thecarrier substrate have an adhesion energy of >30 J/m².
 15. The structureof claim 11 wherein the cured adhesive material is chosen frompolyarylene polymers, cyclic-olefin polymers, arylcyclobutene polymers,and mixtures thereof.